Which of the following is commonly used as the solidifying agent in bacterial nutrient media?

• A. Agar
• B. Pectin
• C. Starch
• D. Gelatin

Answer: (A)

Verified step by step guidance

1. Understand the role of a solidifying agent in bacterial nutrient media: it provides a firm surface for bacteria to grow and form colonies.
2. Review the properties required for an ideal solidifying agent: it should be stable at incubation temperatures, not metabolized by most bacteria, and transparent to observe growth.
3. Evaluate each option based on these criteria: Pectin and Starch are carbohydrates but are often metabolized by bacteria; Gelatin melts at incubation temperatures and can be digested by bacteria.
4. Recognize that Agar is a polysaccharide derived from seaweed, remains solid at typical incubation temperatures (around 37°C), and is not easily degraded by bacteria.
5. Conclude that Agar is the most suitable and commonly used solidifying agent in bacterial nutrient media due to its stability and resistance to bacterial degradation.